Drive mechanisms of the above mentioned type are, for example, described in U.S. Pat. No. 1,339,276. Such drives have been well tried and found to be satisfactory so that they are widely used. Such drives are also used, for example, in so-called straight drawing machines for producing the drawing slide motion. This type of application of the known drives is described in U.S. Pat. No. 3,374,684 (Greven), corresponding to German Utility Model (DE-GM) 1,958,118 and in German Patent (DE-PS) 1,028,067, as well as German Patent 2,322,279. There is room for improvement, however, particularly in connection with the application of such drives for operating the drawing slide in such straight drawing machines. The drive mechanism in such machines must move relatively large masses so that respectively large forces occur, not only during the forward stroke on the one hand, but also during the return stroke, because a rapid return stroke calls for a respectively high slide acceleration. These forces must be transferred by the entraining elements which, as a rule, are entraining rollers engaging the cam or curve surfaces of the driving member. The width of the driving curve or cam track and the roller spacing must be such that the rollers always engage or contact the cam track surface. Without such engagement or contact unacceptably large impacts may occur due to any play that may be present. As a result of such play, the drawing slide may not be entrained anymore until there is again engagement or contact between the respective cam surface and the corresponding entraining roller. The re-establishment of the contact causes the impact because the roller does not move with the respective speed in the respective motion direction of the slide. In order to prevent such impact it may be possible to construct the rollers, or rather their mounting in a position adjustable manner so that the roller position can be adjusted for assuring the desired engagement between the respective cam surfaces. Once cam surface engagement by the roller is established, the roller is fixed in its position. However, such a structure would make it necessary to make the width of the curve along its entire length with an almost infinite precision. Without such infinite precision even a small tolerance in the curve or cam track width could result in the destruction of the roller mounting at any point along the length of the curvature or cam track that does not satisfy the required precision.
In order to avoid such high precision requirements it is known to mount one of two cam follower rollers in a rigid position while the other cam follower roller of the pair is mounted on a spring biased tilting arm which presses the other roller against the respective cam track surface. Thus, it is possible that dimensional tolerances in the cam track can be compensated by the spring biased cam follower roller. Of the two rollers the rigidly mounted roller is one that causes the drawing stroke of the drawing slide. Specifically, this drawing roller is rigidly mounted on the drawing slide to take up the required drawing forces. The other spring biased roller is the one that causes the return stroke of the drawing slide. However, the return stroke is started with a very large acceleration so that the return stroke cam follower roller must also transmit large forces. As a result, the biasing spring of the return stroke cam follower roller must also be dimensioned to be capable to take up these return stroke forces. Such dimensioning of the biasing spring has the undesired consequence that the rollers are always pressed against the respective cam track surface with the correspondingly large forces, whereby these cam follower rollers are exposed to an increased wear and tear which also applies to the roller bearings and to the cam track surfaces. These biasing springs are constructed to be adjustable and if the springs are adjusted to be too soft, unpermissible impacts do occur at the return points or direction reversing points. This is so because the biasing spring that is adjusted to be too soft cannot take up the occurring acceleration forces and hence yields. Such yielding frequently leads to a rapid destruction of machine parts. Such destructions are highly undesirable from a practical point of view so that the biasing spring is preferably adjusted too hard rather than too soft. Thus, it can occur that the biasing spring is compressed into a block so that no spring biasing is possible anymore. In such instances a rapid destruction is also the result because of the above mentioned unavoidable dimensional tolerances in the cam track. Another disadvantage of the spring mounting of the cam follower rollers for the return stroke is seen in that it requires a substantial structural effort and expense.